The holy prophet Muhammad (S.A.W) and his early followers fight against tribal people who worship Idols before he died because all the tribes were against the Holy prophet Muhammad (S.A.W) and his new religion Islam. These tribes feared the increasing power of the new religion practiced by large number of Arab people so for stopping this spreading they fought many wars with the holy prophet Muhammad (S.A.W) and his early followers.
Mostly farming, lumbering, fishing, trading,etc. This required cheap labor, or slaves. They were required for the heavy work to be done quickly by demand.
